SHSAM, SHISAM, and GSAM databases

You typically use simple hierarchical sequential access method (SHSAM), simple hierarchical indexed sequential access method (SHISAM), and generalized sequential access method (GSAM) databases either when converting a non-database system to IMS or when passing data from one application program to another.

When converting from a non-database system to IMS, SHSAM, SHISAM, and GSAM databases allow existing programs, using z/OS® access methods, to remain usable during the conversion to IMS. This is possible because the format of the data in these databases is the same as in the z/OS data sets.

When a database (or non-database) application program passes data to a database (or non-database) application program, it first puts the data in a SHSAM, SHISAM, or GSAM database. The database (or non-database) application program then accesses the data from these databases.

If you have application programs that need access to both IMS and z/OS data sets, you can use SHSAM, SHISAM, or GSAM. Which one you use depends on what functions you need. The following table compares the characteristics and functions available for each of the three types of databases.

Table 1. Comparison of SHSAM, SHISAM, and GSAM databases
Characteristics and functions	SHSAM	SHISAM	GSAM
Uses hierarchical structure	NO	NO	NO
Uses segment prefixes	NO	NO	NO
Supports variable-length records	NO	NO	YES
Supports checkpoint/restart	NO	YES¹	YES¹
Compatible with non-IMS data sets	YES	YES	YES
Supports VSAM as the operating system access method	NO	YES	YES
Supports BSAM as the operating system access method	YES	NO	YES
Accessible from a batch region	YES	YES	YES
Accessible from a batch message processing region	YES	YES	YES
Accessible from a message processing region	YES	YES	NO
Supports logging support	NO	YES	NO
Supports GET calls	YES	YES	YES
Supports ISRT calls	YES²	YES	YES³
Supports CICS®-DBCTL	YES	YES	NO
Supports DCCTL	NO	NO	YES

Note:

Using symbolic checkpoints
To load database only
Allowed only at the end of the data set